Open-hearth furnace



Patented Nov. 1, 1927.

UNITED STATES '1,647,213 PATENT OFFICE Guiones: L. D ANFORTII, JR., OFCHICAGO, ILLINOIS, vAssIGNoIt, BY MESNE ASSIGN- MENTS, To OPEN HEARTHCOMBUSTION COMPANY, OF CHICAGO, ILLINOIS, A OOR- PORATION OF DELAWARE.

OPEN-HEARTH FURNACE.

Application ledJanuary 21, 1921. Serial No. 438,967.

This'invention relates to a new and improved open hearth furnace, andmore particularly to a construction adapted to sointroduce, commingleand direct the entering gases and air 1n an Open hcarth'furnace as toproduce aqquick burning, intensely hot flame adapted `to provide workingheat adjacent the full surface of the metal in the furnace, andfurtheradapted to exhaust the products ofJ combustion through aport ofsmall area with the minimum resistance.

My inycntion comprises an improvement in that portion of an open hearthfurnace 'which relates to the air and gas entrance passages andthe'adjacent portion lof the melting chamber, the remainder of thefurnace. and its appurtenances being O f usual construction, with theaddition that aux1liary means for producing pressure on the incoming'air and draft upon the exhaust may -be used jointly or separately ifdesired under certain circumstances.

As is Well known in open hearth practice, the furnace is double-endedand provided with duplicate regenerating chambers.` The furnace isperiodically reversed in its operation so that the heated exhaust gasesand the incoming gas and comparatively cool in coming air alternatelypass through the re.` generative chambers. The incomingl air and gas arethus heatedto a high temperature before their entrance into the meltingchamber and the heat of the furnace flame is correspondingly increased.

I In furnaces of this character as now generally constructed, the gasand air en ter throughlseparate ports at each end of the meltingchamber, the same ports serving alternately to permit the passage of theoutgoing burnt gases. Valves are provided in after they enter thechamber. The intermixture in general 'occurs gradually as the gases passacross the furnace, the lighter gas gradually rising through andlintermingling With the heavier air, combustion thus gradually takingplace. This results in an unequal heating of the metal in the meltingchamber, and upon Observation of'themetal therein, it Will be noted thatthat portion of the bath adjacent the incoming ports is markedly darkerthan that adjacentthe outgoing ports. The incoming air and gas, althoughpreheated, are not at a temperature adapted to properly operate upon themetal without the additional heat of combustion, and suicient combustiondoes not take place until Well into the meltingchamber from theentrance. Thisaction results in properly heating and melting only aportion of the charge during each reversal of the opera-- tion of thefurnace, that portion adjacent the fuel entry ports not being adequatelyIacted upon. Thus when the furnace is reversed the portion more distantfrom the incoming ports having previously `been permitted to becomerelatively cool must be brought up tothe Working temperature before theproper action takes place. These features of the operation of thefurnace cause` it to Work atv much less than the maximum possibleefficiency.

This late combustion in the melting chamber also results in great heatloss through the exhaust ports and in rapid deterioration of these portsdue to the excessive heat.

Since the same ports serve at different nol periods both as inlet andexit ports and the gases produced by the combustion in the fur' naceexceed in volume the elements produc# ing the combustion, the sizerequired for" i proper passage of the outgoing gases is the major factorin determining the size of the several ports. y

It is an object of the present invention to provide an' open hearthfurnace having a new and improved port construction partieularly adaptedto insure a mixture of the incoming air and gas adequate to secure quickcombustion and thus insure a substantially uniform Operating temperaturethroughout the furnace.

It is a further Object to provide ports of this character whose shape,coacting With the form of the adjacent uportion of the melting chamber,causes the ports, when serving as outlets upon the reversal of thefurnace, to permit and assist in ready passage of the outgoing productsof combustion.

It is an additional object to provide a construction of the characterdescribed which may be applied to existing furnaces without materialalteration therein.

Other and further objects will appear as the description proceeds.

In a specific embodiment, my invention comprises the provision of a gasport with a juxtaposed air port, the ports joining to form a singleeffective port entering the melting chamber. This effective port ,ispreferably less in area than the total area of the several ports joiningto form it and of the passages leading thereto. With this portarrangement, the gas, which enters with a velocity caused by pressure,has an aspirating effect upon the air coming from the adjacent port andthus minimizes any necessity.for the use of auxiliary pressure producingmeans in conection with the incoming air passages, due to theirrelatively small size. This aspirating effect also aids in in-Atermingling the air and gas. The aspirating effect is self-regulatingin that when the gas is introduced under more pressure and consequentlywith greater velocity, more air is induced and with lower gas pressurethe air supplied is correspondingly decreased. The melting chamber isalso provided with necked-down ends adjacent this port.

In ports and passages of this character, although designed withparticular reference 'to mixing the air and gas, the limiting factor isthe provision of proper outlet for the burnt gases. The gasA exhaust maybe caused simply by the usual stack draft or supplemented by mechanicalmeans. Obviously the gases may be borne through practically any type ofport by forced draft, and an economical and 4efficient design will beone wherein the increased draft necessitated does not require anexpenditure of power unwarranted by the increased efciency of operationsecuredby the proper mixing and introduction of the gases. Anotherfactor entering into high draft methods lies in the losses due to coldair being sucked in through the various crevices in the walls of thepassages and chambers. In order to minimize the draft required, I haveprovided a port built upon the lines of a Venturi section, the lateralwalls of the melting chamber convergingtoward the port proper, the roofinclining downwardly and floor sloping upwardly toward the port.Similarly the air and gas ypassages beyond the port also diverge fromthe port, thus providing a reduced port or passageway having similarconv-erging and diverging sections. The greater velocity created inthis. relativ-ely small passageway aids in mixing the air ,and gas andvproduces a flame so directed as to cause the heating of the metal inthe chamber to be accomplished more by convection and less by radiation.

This Venturi section. construction affords not only a proper mixture ofthe incoming air and gas, producing an efficient combustion, but alsosecures the exhaust of the products of combustion without the necessityfor a greatly increased draft in spite ofthe material reduction in theactual port area.

I have illustrated a preferred embodiment of my invention in theaccompanying drawings, inwhich, F igurc l is a fragmentary sectionalelevation of one port portion of an open hearth furnace constructedaccording to my invention; Y y i Figure 2 vis a horizontal section takenon line .2 2 of Figure 1; and

Figure 3 is a sectional plan the kfurnace layout.

The general construction of the regenerative chambers, air and gasvalves and other illustrating associated structures forms no portion ofmy invention and these elements may be of any usual construction.

As shown in the drawing, the gas is led to the furnace from the gasproducers (not shown) by the pipes 14 and passes through the valve 15and passage 16 to the regenerthe roof 5 of the mixing chamber '5;

4In the form of furnace shown the air is forced through the valve 19`into the flue 2() by the fan 23. Means are provided whereby exhaustgases may be shut off from the stack 24 by the damper 25. The damper 26being raised, the gases pass through the passage 27 to the superheater28, then up through the waste heat boiler 29 and down through thesimilar boiler 30, being drawn by the draught fan 81 operated by thesteam turbine 32. The gases then pass up through aflue 33 which leads'upwardly to join the stack 24.

The melting chamber 8 is necked down at 9 and 10 to meet the entrance tothe mixing chamber 5. The angle of the portions 9 and 10 in theparticular structure shown is substantially that of the ports 7. Asshown in Figure 2, the portion 10 has been cooled by water pipes 11 andthe portion 9 by the water container 12. Obviously either or both may becooled in either manner or by any desired cooling construction. Theentrance `of the gas port 4 into the mixing chamber is also cooled withwater circulating pipes 13.

In the operation of the furnace, when an end of the furnace isservingfor inlet 4of air and gas, the heated gas comes through the uptake 3from its regenerative chamber 17 and passes through the port 4 to mixingchamber 5. Simultaneously the heated air comes from its regenerativechamber 21 through the uptakes 6 and passes through the port 7 to themixing chamber 5. As may be understood from reference to Figure l, theair from the two uptakes commingles above the gas inlet port so that inthe mixing chamber the gas stream is intersected by Y van air stream uon both Sides and from above. 'The gas, eing lighter, tends to risethrough the air and it is therefore generally considered unnecessary tosupply air from below the stream of gas. l

The air and gas streams meeting at angles in the chamber 5 interminglesothat las they pass outwardly therefrom at high velocity into thefurnace combustion takes place -at and adjacent the inlet port andworking heat is provided throughout the surface of the metal in themelting chamber. The oppositeend of the furnace is identical -inconstruction to that shown and the burnt gases pass out through theopposite mixing chamber and are divided by the ports, the dividedportions passing down through the air and gas uptakes to the other setof regenerative chambers. The necking down of the meltingv chamber at 9and 10 together with the corresponding increase in area of the ports 4and 7 is of particular importance in facilitating discharge of the burntgases.

Obviously a slight-ly greater draft is required to secure passage of theexhaust gases through the necked mixing chamber than would be necessarywhere the several air and gas ports are of greater area and opendirectly into the furnace., With a furnace of the design shown in thedrawing, however,

this increased draft is but a small portion of the entire draft requiredby the furnace and hence requires no material increase in the draftsupplying means of the furnace. The small increase in power required bythe draft means is very much more than voifset by the increasedefficiency of the furnace.

aThe port may be sodesigned as not to require any draft other than thatnaturally induced in t-he stack, mechanical dra-ft means being providedin the furnace shown primarily because of the draft retarding effect lofthe superheater and the exhaust heat boilers.

The area of the ort between the mixing chamber 5 and melting chamber 8of the furnace is to a degree self-regulating in that in a new furnacewith clean checkerwork and no obstructions in the several fines anduptakes, the resistance oifered to the passage of the exhaust gases bythese elements is at its lowest, and at'the same time the area of theport is at its minimum. As the furnace operation continues, thecheckerwork and flues become somewhat obstructed with flue dirt, therebyincreasing the resistance to t-he gases and at the same time the brickwork forming the port is gradually worn away, thus increasing the areaof the port. In this way the resistance offered by the port decreases asthat offered by the checkerwork and flues increases. f.'

An important advantage ofthe construction of the present inventionconsists in the fact that since the air is adequately mixedwith the.fuel it is not necessary to use the large excess of air required in theconventional.type of furnace in order vto secure complete combusti-on.This elimination of excess air avoids the loss due tothe necessity ofheating and exhausting this air and further has abeneficial effect inthat there is no over-oxidation of the product of the furnace. As hasbeen stated, the aspirating or Siphon effectl of the incoming gas streamupon the air renders the quantity of air used lsubstantiallself-regulating.

IVith a furnace constructed according to my invention and operated asdescribed, it has been found that production can be inicreasedapproximately twenty per cent, and

the consumption of lfuel per ton of product correspondingly decreased.The cost'o'f operating items chargeable against each ton of product isvery materially decreased..

While the specificy construction shown and described herein isparticularly adapted to provide in furnaces using producer gas, a mixingchamber and relatively small incoming port commonl to the air and fuel,together with means for introducing the fuel and air thereto, impellingthem into a desirable mixture, causing combustion which pro` videsworking temperature throughout the surfaceof the metal, and thenadequately exhausting the waste products of combustion, it is to beunderstood that. changes may be made in the details of construction toadapt the invention to varying working conditions and uses. For example,for application to furnaces using other than producer gas for fuel, theseveral elements will be modified as necessary for the utilization ofthe par- 1 -in size from said uptakes to an air port located adjacentthe gas port, and the lateral Walls being bowed inwardly to form ay mix`ing chamber into which said ports discharge, the mixing chamber beingprovlded with a port into the melt-ing chamber, this port having asmaller area than the combined areas of the gas and air ports.

2. In an open hearth furnace, gas and air ports at either end,thelateral Walls being bowed inwardly adjacent said ports, the

space between the opposed bowed portions being greater in area than thegas port, and less in area than'the combined areas of the gas and airports.

3." In an open hearth furnace, a melting chamber, air and gas passages'entering either end of the chamber through a restricted port, thepassages and the adjacent portion of the melting chamber being sorelated to the port as to form approximately a Venturi section wherebymovement of gases through the port is facilitated.

4. In'an open hearth furnace, a melting chamber, air and gas passagesentering either end of the chamber through a re- A'stricted port, thepassages and the floor, roof and lateral walls of the melting chamberbeing so related to the port as to form ap-.

proximately a Venturi section whereby movement of gases in eitherdirection through the portl is facilitated.v

5. The method of operating an open hearth furnace which consists inconducting combustion within said melting chamber,

and gradually expanding the' area of the stream of the products ofcombustion after withdrawal from' the melting chamber, whereby saidproducts of combustion will pass from said melting chamber at relativelyhigh velocity. e

6. The method vof operating an open hearth furnace which consists inconducting heated air in a stream gradually decreasing incross-sectional area into union with a stream of fuel to produce acombustible mixture, contracting the area of said mixture to less thanthe combined areas ofthe streams of said air and fuel prior to theirunion, gradually expanding the area of said mixture in the meltingchamber of said furnace, burning said mixture within said meltingchamber, gradually contracting the area. of the stream of the productsof combustion within said melt-ing chamber, and gradually expandingthearea of they stream of the products of combustion after Withdrawal fromthe melting chamber, whereby said products of combustion will pass fromsaid melting chamber at relatively high velocity.

7. The method of operating an open hearth furnace, which consists inconducting a heated gas in a stream gradually decreasing incross-sectional area into union with a stream of fluid to produce acombustible mixture, contracting the area of said mixture to less thanthe combined areas ofthe streams of said gas and fluid prior to theirunion, gradually expanding the area of said mixture in the meltingchamber of said furnace, and burning said mixture within said meltingchamber.

8. The method of' operating an open hearth furnace which consists inconducting air in a. stream gradually decreasing in cross-sectional areainto union with a stream of fuel to produce a combustible mixture;contracting the area of-said mixture, to less than the combined areas ofthe streams of said air and fuel prior to their union; graduallyexpanding the area of said mixture in the melting chamberof saidfurnace, and burning said mixture within said melting chamber.

9. The method of operating an open hearth furnace which consists inconducting heated air in a stream gradually decreasing incross-sectional area into union with a stream of fuel to produce acombustible mixture, gradually reducing the area of the stream of. saidmixture, gradually expanding the area of said mixture in the meltingchamber of said furnace, burning said mixture within saidl meltingchamber, gradually contracting the area of the stream of the products ofcombustion within said melting chamber, and gradually expanding the areaof the stream of the products of combustion after withdrawal from/themelting chamberg/lU-" whereby said products of combustion will pass fromsaid melting chamber at relatively high velocity. l l

10. In an open hearth furnace,a melting chamber, air and gasregeneratorsand slag pockets, port ends connecting the slag 4pockets and meltingchamber, each port end comprising a mixing chamber provided with a portdischarging into the melting chamber, gas and air ports discharging intothe mixing chamber, passages leading to said gas and air ports andapproximately vertical ,passages connecting the first named passages andthe slag pockets, the area of the port between the mixing and meltingchambers beingless than the combined areas of the approximately verticalpassages, the walls on'both sides of the port between the mixing andmelting chambers inclining to form approximately a Venturi section.

Signed at Chicago, Illinois, this 4th day of January, 1921.

VGEO. L; DANFORTH, JR.

